The construction of metal building systems, often referred to as “pre-engineered” metal buildings systems, includes building systems comprised of metal structural members (structural wall columns, corner columns and roof support members) with horizontal metal wall girts and metal roof purlins covered by integrally faced/laminated vapor barrier fiberglass blanket insulation and exterior metal cladding. The majority of these metal building systems incorporate what is commonly known as a by-pass wall girt design, in which the building support perimeter columns and main roof support members are installed followed by horizontal, parallel spaced wall girts installations which are bolted exterior to the columns and thus by-pass, and often lap over, the exterior column locations. At the roof, the main roof support members (sometimes termed rafters or rake beams) have parallel spaced roof purlins attached above the roof support members, oriented normal to the direction of the roof support members. A typical prior art steel structural frame of this nature is shown in FIG. 1, in which the perimeter column and main roof support members are shown as I-beams, and the wall girts and roof purlins are shown as generally Z-shaped metal channel members. FIG. 1 also shows a typical prior art eave purlin at the roof side wall edge and a building base C-channel at the wall base. This building system is generally used by many of the commercial manufacturers of pre-engineered building systems, including Butler, Robertson, Ceco, Varco Prudin and American.
In these prior art systems, following the installation of the above-described steel structural framework, the horizontal wall girts are covered by firstly positioning in vertical orientation, suspended from the eave, integrally faced/laminated vapor barrier fiberglass blanket. This blanket insulation is installed exterior to the wall girts and roof purlins, with the vapor barrier facing inwardly, as can be seen in FIG. 1. The exterior metal cladding, such as sheet metal, is then installed over the blanket insulation. The metal cladding is then mechanically secured in place by drilling through the metal cladding, through the blanket insulation and the interior vapor barrier facing into the wall girts. The fasteners are screws with compressive washers. The screws are tightened sufficiently to compress the washers to prevent the ingress of moisture through the screw holes. The roof is similarly insulated by installing the interior faced blanket insulation above the roof purlins prior to applying the exterior metal cladding. The cladding is secured by drilling through the cladding and insulation and mechanically securing to the roof purlins with similar screw fasteners and compressive washers.
The tightening of the screws causes compression of the laminated vapor barrier insulation material between the cladding and wall girts, and between the cladding and roof purlins. This compression substantially reduces the heat insulating properties of the blanket insulation along each attachment line. For instance, a 6 inch R20 insulation can drop to only about R10 or R12 due to these compression points. One prior art approach to address the problem of compression of the insulation at the wall girts is shown in U.S. Pat. No. 4,346,543 issued Aug. 31, 1982 to Wilson et al. This patent describes the use of higher compressive strength insulation between the wall girt and the exterior metal cladding. U-channel members are also used exterior of the wall girts to hold the blanket insulation without compression. However, the patent still relies on exterior installation of the blanket insulation, which has the problems mentioned below.
In the past, the maximum thickness and corresponding RSI value of the wall insulation applied in blanket form has been functionally limited to 6 inches due to a number of factors, including:
a) the difficulty in compressing heavier insulations without significant deformation of the metal cladding; and
b) the weight of heavier insulation becoming difficult to manually support.
The prior art insulation systems are additionally problematic when the insulation must be installed in poor weather conditions, particularly during windy or rainy conditions. Since the insulation is installed prior to closing in the building with the exterior metal cladding, the insulation and workers are exposed to the environmental elements. The blanket insulation can act similar to a sail catching wind, which causes the significant delays during erection. During periods of significant rainfall the exposed insulation becomes saturated with moisture damaging the insulation and thermal effectiveness.
As well, the prior art building installation and insulation methods leave the horizontal wall girts exposed on the interior of the building space. Being horizontal the exposed girts become home for dust and debris creating a home for interior environmental contaminants and refuge for dust mites and vermin.
There is a need for an improved insulation method and system which facilitates the following:
a) installation of blanket insulation from the interior of the building space, into the building framework, in a generally uncompressed form, for the full depth of the horizontal wall girt to maximize the thermal effectiveness of the wall insulation system;
b) increased building erection efficiencies by incorporating a system less prone to weather delays or damage; and
c) reducing the exposed horizontal wall girt condition on the interior of the building space.